Methods of and devices for enhancing communications that use spread spectrum technology by using variable power techniques

ABSTRACT

We have invented methods of and devices for introducing unequal error protection into spread spectrum communication systems. One embodiment of the invention addresses certain inefficiencies of the standard known as IS-95 used, for example, in some mobile direct sequence code division multiple access (&#34;DS-CDMA&#34;) phone systems. The invention allows for increased system capacity and/or improved quality. More specifically, spread spectrum multiple access (&#34;SSMA&#34;) coding may be combined with the concept of unequal error protection (&#34;UEP&#34;), resulting in an UEP SSMA coding process. IS-95, in order to make significant portions of a signal highly immune to errors, has imposed the same high degree of error immunity on less significant portions of the signal (when, in fact, a lower degree would suffice) and, thus, wastes bandwidth. The present invention&#39;s coding process (i.e., UEP SSMA) utilizes bandwidth in a closer to optimal manner than known methods.

This is a Continuation of application Ser. No. 08/815,284 filed Mar. 11,1997, now U.S. Pat. No. 5,799,013, which in turn is a Rule 62Continuation of application Ser. No. 08/235,577, filed Apr. 29, 1994 nowabandoned. The entire disclosure of the prior application(s) is herebyincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to communication of signals withuse of spread spectrum (SS) technology. More specifically, the presentinvention relates to improving spread spectrum system capacity and/ortransmission quality.

BACKGROUND OF THE INVENTION

Spread spectrum multiple access (SSMA) techniques are attractingwidespread attention in the personal communication fields, such as, forexample, digital cellular radio. In SSMA systems, both the time andfrequency domains may be shared by multiple users simultaneously. Thissimultaneous sharing of time and frequency domains is to bedistinguished from time-division and frequency-division multiple accesssystems, TDMA and FDMA, where multiple user communication is facilitatedwith use of unique time slots or frequency bands, respectively, for eachuser.

In SSMA systems, such as direct-sequence code division multiple access(DS-CDMA) cellular systems, a base station may simultaneously transmitdistinct information signals to separate users using a single band offrequencies. Individual information signals simultaneously transmittedin one frequency band may be identified and isolated by each receivinguser because of the base station's utilization of a unique spreadingsequence in the transmission of each information signal. Prior totransmission, the base station multiplies each information signal by aspreading sequence signal assigned to the user intended to receive thesignal. This multiplication, performed by a "spreader," "spreads" thespectrum of the information signal over a "wide" frequency band sharedby all users. To recover the correct signal from among those signalstransmitted simultaneously in the wide frequency band, a receivingmobile user multiplies a received signal (containing all transmittedsignals) by its own unique spreading sequence signal and integrates theresult. These operations are performed by a "despreader." By so doing,the user "despreads" the received signals and identifies that signalintended for it, as distinct from other signals intended for otherusers.

The Telecommunications Institute of America ("TIA") recently adopted aSSMA standard that implements DS-CDMA technology. TelecommunicationsInstitute of America, "Mobile Station-Base Station CompatibilityStandard for Dual-Mode Wideband Spread-Spectrum Cellular System," 1993(published as IS-95). This standard is called IS-95. However, we haverecognized that spread spectrum systems, such as that described in theIS-95 standard, process certain signals inefficiently. This inefficientprocessing results in reduced system capacity and/or signal quality.

SUMMARY OF THE INVENTION

We have invented a spread spectrum transmission technique which allowsfor increased system capacity and/or improved signal quality. Thesebenefits are obtained by employing unequal error protection (UEP) in aspread spectrum system.

In accordance with illustrative embodiments of the present invention, asignal to be communicated by a spread spectrum system multiple accesssystem comprises at least two portions having differing levelssignificance relative to each other. Illustratively, these differinglevels of significance reflect differing levels of sensitivity to signalerrors. A first of these portions represents information which isrelatively sensitive to signal errors suffered in transmission, while asecond of these portions represents information which is relativelyinsensitive to such signal errors. Because of this difference inrelative error sensitivity, these portions are processed with distincterror protection processes which supply greater and lesser degrees oferror protection, respectively, to these portions.

Embodiments of the present invention make efficient use of availablechannel bandwidth because, unlike conventional spread spectrum systemsemploying error protection (such as the IS-95 standard), the embodimentstailor error protection capability to signal error sensitivity. TheIS-95 standard, for example, employs an error protection process whichis suitable to the most error-sensitive portion(s) of the signal. Thus,IS-95 provides a degree of error protection to some portions of thesignal which exceeds that which is needed for such portions. Thisexcessive degree of error protection (sometimes referred to as"over-coding") wastes channel bandwidth.

The present invention, on the other hand, utilizes channel bandwidth ina more efficient manner through a tailored approach to error protection.Thus, for a given channel bandwidth, the present invention affordsgreater system capacity. For a given channel bandwidth and a givennumber of users, the present invention affords enhanced communicatedsignal quality. Naturally, embodiments of the present invention mayprovide both enhanced system capacity and enhanced signal quality.

An example of a signal exhibiting at least two portions having differinglevels significance relative to each other is a compressed speechsignal. As is well known in the art of speech compression, a compressedspeech signal comprises a sequence of frames, wherein each frametypically represents 20-30 ms of uncompressed speech. A frame ofcompressed speech comprises a set of bit-fields. Each such bit-fieldrepresents parameters needed to reconstruct speech from the compressedframe. For example, these bit-fields typically represent parameters suchas linear prediction coefficients, pitch, codebook indices, and codebookgains. In the context of the present invention, these bit-fields areillustrative portions of the compressed speech signal which havediffering levels of significance. Another example of a signal whichincludes portions having differing levels of significance is a signalwhich represents distinct types of information, such as audioinformation and alphanumeric information. In this case, the audioportion and the alphanumeric portion have different levels ofsignificance. Thus, the present invention may be applied to signals suchas these to enhance SS system capacity and/or quality.

Those of ordinary skill in the art will appreciate that the principlesof the present invention are applicable to a wide variety of SS signalsand systems. For example, the present invention may be applied toprovide tailored error protection capability where the signal to becommunicated includes more than two portions of differing sensitivity toerrors (e.g., a signal may include a first portion(s) which is (are)relatively sensitive to signal errors, a second portion(s) which is(are) relatively moderately sensitive to signal errors, and a thirdportion(s) which is (are) relatively insensitive to signal errors).While the illustrative embodiments of the present invention concern aDS-CDMA, the present invention is applicable to systems which employother SS communication techniques (including frequency hopping ("FH")systems, time hopping ("TH") systems, chirp systems and single userversions of the other above-mentioned multiple access systems). Inaddition, though the illustrative embodiments concern a wirelesscommunication channel of the type addressed by the IS-95 standard, thepresent invention may be applied to SSMA systems with other types ofchannels such as, for example, optical fiber channels, cabletransmission channels, infrared wireless channels, and optical freespace channels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents an illustrative system in which a UEP DS-CDMA codingprocess is implemented.

FIG. 2 presents a block diagram of an illustrative UEP DS-CDMA encodermade in accordance with the present invention.

FIG. 3 presents a detailed block diagram of the illustrative UEP DS-CDMAencoder of FIG. 2.

FIGS. 4a through 4h present how a signal is processed by theillustrative UEP DS-CDMA encoder of FIG. 3 as compared with a CDMAencoder without UEP.

FIG. 5A presents a block diagram of an illustrative UEP DS-CDMA decoderfor use in conjunction with the UEP DS-CDMA encoder of FIG. 3.

FIG. 5B presents a detailed block diagram of an illustrative UEP DS-CDMAdecoder of FIG. 5A.

FIG. 6 presents a detailed block diagram of a second illustrative UEPDS-CDMA encoder made in accordance with the present invention.

FIGS. 7a through 7d present how a signal may be processed by the UEPDS-CDMA encoder of FIG. 6.

FIG. 8 presents a block diagram of a second illustrative UEP DS-CDMAdecoder for use in conjunction with the UEP DS-CDMA encoder of FIG. 6.

FIG. 9 shows a detailed block diagram of the UEP DS-CDMA decoder of FIG.8.

FIG. 10 shows a detailed block diagram of a third illustrative UEPDS-CDMA encoder made in accordance with the present invention.

FIG. 11 shows a detailed block diagram of a third illustrative UEPDS-CDMA decoder that may be used in conjunction with the UEP DS-CDMAencoder of FIG. 10.

FIG. 12 shows a variation of UEP DS-CDMA encoder of FIG. 10.

DETAILED DESCRIPTION OF THE ILLUSTRATION EMBODIMENTS

The "Detailed Description" will be described in a wireless UEP DS-CDMAtelephony application environment showing only one base station forpurposes of simplicity. However, those skilled in the art willappreciate that the present invention may be used with many differenttypes of SS systems, many different types of applications, and/or manydifferent types of channels.

The illustrative embodiments of the invention are presented in thecontext of communicating compressed speech signals. As is well known inthe art of speech compression, a compressed speech signal comprises asequence of frames, wherein each frame typically represents 20-30 ms ofuncompressed speech. A frame of compressed speech comprises a set ofbit-fields. Each such bit-field represents parameters needed toreconstruct speech from the compressed frame. For example, thesebit-fields typically represent parameters such as linear predictioncoefficients, pitch, codebook indices, and codebook gains. See U.S.patent application Ser. No. 08/179,831, of B. Kleijn entitled "Methodand Apparatus for Prototype Waveform Speech Coding," which is assignedto the assignee of the present invention. In the context of the presentinvention, these bit-fields are illustrative portions of the compressedspeech signal which have differing levels of significance. The bit-fieldrepresenting pitch is an example of a more significant portion of thesignal as opposed to some other bit-fields of the frame. The packing andunpacking of bit-fields in speech coding are conventional in the art.For clarity of explanation of the embodiments, therefore, no details ofthe packing and unpacking of bit-fields (illustrative "portions") willbe presented.

For clarity of explanation, the illustrative embodiments of the presentinvention are presented as comprising individual functional blocks(including functional blocks labeled as "processors"). The functionsthese blocks represent may be provided through the use of either sharedor dedicated hardware, including, but not limited to, hardware capableof executing software. Use of the term "processor" should not beconstrued to refer exclusively to hardware capable of executingsoftware.

Illustrative embodiments may comprise digital signal processor (DSP)hardware, such as the AT&T DSP16 or DSP32C, read-only memory (ROM) forstoring software performing the operations discussed below, and randomaccess memory (RAM) for storing DSP results. Very large scaleintegration (VLSI) hardware embodiments, as well as custom VLSIcircuitry in combination with a general purpose DSP circuit, may also beprovided.

FIG. 1 shows a system in which the UEP-DS-CDMA coding scheme may beimplemented. The system includes a base station 100, a public switchedtelephone network 102 ("PSTN 102"), a plurality of mobile units, e.g.,104a and 104b, and a plurality of stationary units, e.g., 106a and 106b.Base station 100 includes a UEP-DS-CDMA transmitter 108, a UEP-DS-CDMAreceiver 110, and an antenna 112. Mobile unit 104a includes aUEP-DS-CDMA transmitter 108a, a UEP-DS-CDMA receiver 110a, and anantenna 114. Mobile unit 104b includes a UEP-DS-CDM transmitter 108b, aUEP-DS-CDMA receiver 110b, and an antenna 116. Mobile units 104a and104b may, for example, communicate with stationary units 106a and 106bvia the base station 100, a link 118 between the base station 100 andthe PSTN 102, and the PSTN 102.

Again referring to FIG. 1, if a first person in mobile unit 104a desiresto talk with a second person located at stationary unit 106a, the firstperson places a call. The UEP-DS-CDMA transmitter 108a encodes andtransmits signals representative of the first person's voice. TheUEP-DS-CMA receiver 110 of the base station 100 receives and decodes thesignal representative of the first person's voice. Next, the UEP-DS-CDMAtransmitter 110 takes the decoded voice and transmits it to stationaryunit 106a. Voice signals from the second person to the first personwould also be sent via the PSTN and base station 100. Thus, the firstperson and the second person are able to communicate.

Those skilled in the art will realize that although only one type ofcommunication has been described, there are many other manners ofcommunicating in which the present invention may be used. For example,mobile unit 104a may wish to communicate with another mobile unit 104b.This may require more than one base station if, for instance, the mobileunits are far apart. Further, the present invention may be used totransmit/receive communications wherein satellites are involved.Additionally, the present invention may be used in systems whereininformation other than signals representing voice are transmitted andreceived. For example, one may transmit/receive data relating to otheraudio signals, video signals, audio-video signals, and other types ofsignals. All this having been mentioned, we will now focus upon how UEPmay be applied in a UEP-DS-CDMA system for voice communications.

FIG. 2 shows a block diagram of a UEP-DS-CDMA transmitter 108. TheUEP-DS-CDMA transmitter 108 includes a pre-processor 200, a UEPprocessor 202, and a post-processor 204.

FIG. 2 may be implemented in a variety of manners. For instance, FIG. 2may be implemented using a variable time ("VT") UEP method, a variablecode ("VC") UEP method, or a variable power ("VP") UEP method. Also,FIG. 2 may be implemented using combinations of the above three methods.However, a common thread amongst the above methods is that they allapply a first error protection process to a set of more significantportions of a signal and a second error protection scheme to a set ofless significant portions of the signal. Further, since the first errorprotection scheme provides a greater amount of error protection than thesecond error protection scheme, unequal error protection, or UEP, isachieved within the DS-CDMA coding scheme.

After describing the VT method that may be used in the framework of theUEP-DS-CDMA transmitter 108 shown in FIG. 2, a corresponding UEP-DS-CDMAreceiver using VT methods will be described. Next, a VC method that maybe used in the framework of the UEP-DS-CDMA transmitter 108 shown inFIG. 2, a corresponding UEP-DS-CDMA receiver using VC methods will bedescribed. Next, a VP method that may be used in the framework of theUEP-DS-CDMA transmitter 108 shown in FIG. 2, a corresponding UEP-DS-CDMAreceiver using VP methods will be described. Finally, combinations ofthe VT, VP, and VC methods will be briefly described.

1. UEP-DS-CDMA Transmitter: The VT UEP Method and Device

FIG. 3 shows a detailed block diagram of a UEP-DS-CDMA transmitter 108that may be used in with the VT method. The pre-processor 200, the UEPprocessor 202, and the post-processor 204 will be described in order.

The pre-processor comprises input voice data interface 300, a firstchannel coder 302, and a second channel coder 304. The interface 300 mayuse any one of a number of voice compression techniques. However, itserves to input voice data. Interface 300 separates voice data into twodata streams of unequal significance. The relevance of the unequalsignificance to UEP will be described in detail later. A first datastream 306 (e.g., a more significant data stream) is input into thefirst channel coder 302 and a second data stream 308 (e.g., a lesssignificant data stream) is input into the second channel coder 304. Thefirst channel coder 302 and the second channel coder 304 essentiallyserve to build redundancies into the first data stream 306 and thesecond data stream 308 to form a first channel coded data stream 310 anda second channel coded data stream 312, respectively. The first channelcoded data stream 310 and the second channel coded data stream 312 areinput into the UEP processor 202.

The UEP processor 202 takes, as its inputs, the first channel coded datastream 310 and the second channel coded data stream 312 and uses a firstvariable time modulator 313 and a second variable time modulator 315.The variable time modulators, 313 and 315, generate a first timemodulated signal 314 and a second time modulated signal 316,respectively, from the first channel coded data stream 310 and thesecond channel coded data stream 312, respectively. The first timemodulated signal 314 and the second time modulated signal 316 are thenprocessed further in the post-processor 204.

The post-processor 204 takes, as its inputs, the first time modulatedsignal 314 and the second time modulated signal 316 and outputs an RFsignal representing voice data input by the means for inputting voicedata 300. The post-processor comprises a multiplexer 318, an interleaver320, a spreader 322, a modulator 324, a radio frequency ("RF")transmitter 326, and an antenna 328, all connected as shown. Themultiplexer 318 functions to combine the first time modulated signal 314and the second time modulated signal 316. The combined signal is theninterleaved by the interleaver 320. The processing that occurs in themultiplexer 318, the spreader 322, the modulator 324 and the RFtransmitter 326 is the type of processing typical of DS-CDMA systemsknown to those skilled in the art. For example, the spreader 322 takesas one input a spreading sequence 323. The type of processing thatoccurs in the interleaver 320 will be discussed later.

Referring to FIG. 3, the input voice data interface 300 separates thesignal, e.g., voice data, into the first data stream 306 and the seconddata stream 308. The first data stream 306 comprises at least one "more"significant portion of the voice data and the second data streamcomprises at least one "less" significant portion of the voice data. Theat least one more significant portion is also referred to as a firstsegment. The at least one less significant portion is also referred toas a second segment. The interface 300 performs this separation basedupon the significance of the time portion of the voice data. The firstsegment of the signal is said to be more significant than the secondsegment of the signal if, for example, the first segment is moresensitive to transmission errors. The first segment and the secondsegment may either be digital or analog. Thus, for example, the firstdata stream 306 may comprise information bits that are deemed to be moresignificant than the second data stream 308. In this situation, thefirst segment and the second segment may be referred to as a set of moresignificant bits and a set of less significant bits, respectively.

FIGS. 4a through 4f and 4h show how a signal is processed by the encodershown in FIG. 3, through the variable time modulators, 313 and 315. Asan example, FIGS. 4a and 4b show both the first data stream 306 and thesecond data stream 308 as being two bits in length. The first channelcoder 302 and the second channel coder 304 are each rate one-halfcoders. Therefore, when processed by the coders 302, 304, the number ofbits in streams 306 and 308 are doubled at the output of coders 302, 304(see, e.g., FIGS. 4c and 4d). Although the first channel coder 302 andsecond channel coder 304 are of the same rate, the reason why twodistinct channel coders are used is to provide a clear demarcationbetween the more significant portions and the less significant portions.In order to maintain this demarcation, two channel decoders will be usedin the receiver 110.

When shown in the time domain (FIGS. 4a and 4b), the first data stream306 and the second data stream 308 are each eight basic time units long.A "basic time unit" is the longest time interval, T₀, such that"stretched" bits (see FIG. 4e and accompanying discussion below)representing the first segment and "compressed" bits (see FIG. 4f andaccompanying discussion below) representing the second segment areinteger multiples of T₀. Thus, if UEP were not used, the informationshown in FIGS. 4a and 4b would be, collectively, sixteen basic timeunits long (as opposed to splitting the sixteen basic time units of bitsinto eight more important basic time units of bits and eight lessimportant basic time units of bits). More generally, the first datastream 306, comprising a set of more significant bits, is represented ina first time portion 350 (e.g., eight basic time units). The second datastream 308, comprising a set of less significant bits, is represented ina second time portion 352 (e.g., eight basic time units). At least oneof these time portions, 350 and/or 352, is time modulated. Onceprocessed by the first channel coder 302 and second channel coder 304,the set of more significant bits would be time modulated to increase(e.g., stretch) the first time portion or the set of less significantbits would be time modulated to decrease (e.g., compress) the secondtime portion, respectively, or both. The result of the time modulationis called a modulated frame 354, as shown in FIG. 4h. While themodulated frame 354 is shown, for simplicity, as being generated from afour bit frame (see FIGS. 4a and 4b), typically, frames comprisesignificantly more bits than four, as is apparent to those skilled inthe art.

Referring to FIGS. 4c and 4d, the first channel coded data stream 310and the second channel coded data stream 312 are shown, respectively. Inthis example, the first channel coder 302 and the second channel coder304 take the first data stream 306 and the second data stream 308,respectively, and use two bits to represent each information bittherein. Thus, both FIGS. 4c and 4d are shown as having four bits each.When twice as many bits occur in the first and second channel coded datastreams 310 and 312 as compared to the first and second data streams,the first and second channel coders 302 and 304 are be referred to as"rate 1/2 coders." Another example would be one wherein the first andsecond channel coded data streams had three times as many bits as thefirst and second data streams. In this example, the first and secondchannel coders are "rate 1/3 coders."

Referring to FIGS. 4e through 4h, the effect of time modulation isshown. FIGS. 4e and 4f show the first time modulated signal 314 and thesecond time modulated signal 316, respectively. Although the first andsecond time modulated signals, 314 and 316, represent two original bits(see FIGS. 4a and 4b), the first time modulated signal 314 and thesecond time modulated signal 316 are shown as being twelve and fourbasic time units in length, respectively, as shown in FIG. 4h, insteadof eight time bits each as shown in FIG. 4g.

If time modulation were not performed, an input to the spreader 322would look similar to FIG. 4g wherein the first channel coded datastream 310 and the second channel coded data stream 312 are combined. Infact, in this situation, one would most likely have only one channelcoder, not two, and there would be no need for the multiplexer 318.Further, in this situation, even if the bits of FIG. 4a were moresignificant than the bits of FIG. 4b (unbeknownst to the channel coder),the two bits shown in FIG. 4a would have eight basic time units devotedto them prior to being input into the spreader 322. Also, the two bitsshown in FIG. 4b would have eight basic time units devoted to them priorto being input into the spreader 322.

However, when time modulation is performed, preferably, it has theeffect of "stretching" the more significant bits and "compressing" theless significant bits as determined by the interface 300. Timemodulators 313, 315 may be implemented in software by conventionaltime-index scaling procedures. Illustratively, the number of basic timeunits used to represent a more significant bit is greater than thenumber of basic time units to represent a less significant bit. Thoseskilled in the art will realize, however, that the processing of thesignal shown in FIG. 4 is only exemplary and that one could:

(a) use a single channel coder that is time-shared between the moresignificant bits and the less significant bits;

(b) use no channel coder, in which case the more significant bits andless significant bits would be input directly into, e.g., the firstvariable time modulator 313 and the second variable time modulator 315;

(c) have more than two levels of significant bits (e.g., a first, secondand third level of significance) wherein each level has a differentamount of error protection provided to it;

(d) have the first channel coder 302 be of a given rate and the secondchannel coder 304 be the same rate (but not necessarily each being arate 1/2 coder);

(e) have any percentage of the bits (as opposed to 50% shown in FIG. 4)be deemed "more significant" depending upon the application and thecapabilities of the interface 300;

(f) stretch the more significant bits while leaving the less significantbits unchanged or compress the less significant bits while leaving themore significant bits unchanged; and/or

(g) combinations of the above that do not conflict such as "(e)" and"(f)."

Preferably, the interleaver 320 symbol length is the basic time unit andthus, the interleaver 320 operates upon each basic time unit of thesignal shown in FIG. 4h. However, those skilled in the art will realizethat one could have the interleaver 320 operate on symbols wherein thesymbol length is the length of:

(a) a chip, wherein a chip may be defined as the time associated withone symbol unit of the direct sequence spreading sequence and whereinthe interleaving process performed by the interleaver 320 is performedsubsequent to the spreading function of the spreader 322;

(b) a multiple integer of a chip or the basic time unit; and/or

(c) non-integer multiples of the chip or the basic time unit.

Also, the interleaver 320 may interleave its input signal maintainingthe variable symbol time lengths of the individual stretched andcompressed bits represented by FIGS. 4e and 4f, regardless of whetherthe stretched and compressed bits have a common basic time unit.Although in the case of using no channel coders interleaving may not berequired, interleaving over the basic time unit provides extraprotection against fading.

The output of the interleaver goes into the spreader 322. The spreader322 represents a typical spreader for DS-CDMA applications as describedin K. S. Gilhousen, I. M. Jacobs, R. Padovani, A. J. Viterbi, L. A.Weaver, Jr., and C. E. Wheatley III, "On the Capacity of a Cellular CDMASystem," IEEE Transactions of Vehicular Technology, vol. 40, no. 2,303-312 (May, 1991) (hereinafter "the Gilhousen et al. article"). Themodulator 324, the RF transmitter 326, and the antenna 328 are alsotypical of such elements as mentioned in the Gilhousen et al. article.

Preferably, for the case of orthogonal transmission using, e.g., Walshfunctions (see the Gilhousen et al. article), a Walsh modulator basedupon, e.g., the basic time unit, T₀, is, for example, interposed betweenthe UEP DS-CDMA transmitter's interleaver 320 and spreader 322. Also,the first channel coder 302 and the second channel coder 304 may beconvolutional coders or block coders. The interleaver 320 may be a blockinterleaver or a convolutional interleaver. Standard timing signals areprovided inside the transmitter, e.g., 108 of FIG. 1, for the relevantunits. Orthogonal transmission and standard timing signals may also beused with VC transmitters and VP transmitters which are described insection "3." and section "5." of this detailed description,respectively.

2. UEP-DS-CDMA Receiver: The VT UEP Method and Device

FIG. 5A shows a block diagram of a UEP-DS-CDMA receiver 110. TheUEP-DS-CDMA receiver 110 comprises a pre-processor 500, a UEP processor502, and a post-processor 504. The pre-processor 500, the UEP processor502, and the post-processor 504 will be described in order withreference to FIG. 6 which shows a receiver that may be used with thetransmitter of FIG. 3.

Referring to FIG. 5B, the pre-processor 500 comprises an antenna 506, anRF receiver 508, and a demodulator 510 all connected as shown. Theoutput of the demodulator 510 is input into the UEP processor 502.

The UEP processor comprises a despreader 512, a deinterleaver 514, ademultiplexer 516, a first accumulator 518, and a second accumulator520, all connected as shown. Those skilled in the art are familiar withhow to implement conventional synchronization and timing schemesassociated with DS-CDMA systems. See the Gilhousen et al. article. Thesesynchronization and timing schemes have already been applied in thepre-processor 500 and thus, the UEP processor receives properly timedand synchronized signals ("the timed signals").

The despreader 512 receives a signal 528 and outputs a despread signal530. The despreader 512 accomplishes this function by correlating thesignal 528 with the spreading sequence 532 over each basic time unit.The despread signal 530 represents analog values that, when properlycombined, form a series of soft decision values. The manner in whichthese analog values may be combined will now be explained.

The deinterleaver 514 receives the despread signal 530 and outputs adeinterleaved signal 534. The deinterleaver 514 thus functions toperform an inverse operation of that performed by the interleaver 320 ofthe transmitter 108. Thus, the order of the basic time units of thesignal input into the interleaver 320 is restored. However, theamplitude of the signal in the receiver 110 is, in general, analog, thusdeinterleaver 514 performs "soft" deinterleaver operations.

The demultiplexer 516 receives the deinterleaved signal 534 and outputsa first set of time domain portions corresponding to the set of moresignificant bits and a second set of time domain portions correspondingto the set of less significant bits. Both the first set and second setof time domain portions comprise analog values that were represented bythe despread signal 530.

The first accumulator 518 receives the first set of time domainportions. The first accumulator 518 operates upon the analog valueassociated with each basic time unit for each stretched bit. Forexample, in FIG. 4e, there are three analog values per stretched bitsince each stretched bit occupies three basic time units. These analogvalues are added together, resulting in a soft decision value for eachstretched bit. Once this is done for all of the stretched bits, itresults in a series of soft decision values representing the first setof time domain portions.

The second accumulator 520 receives the second set of time domainportions. The second accumulator 520 operates upon the analog valueassociated with each basic time unit for each compressed bit. Forexample, in FIG. 4f, there is one analog value for each compressed bitsince each stretched bit occupies one basic time unit. Although ingeneral analog values are added together as discussed with reference toFIG. 4e, no addition is necessary in the special case of only one analogvalue per compressed bit as shown in FIG. 4f. This results in a softdecision value for each compressed bit. Once this is done for allcompressed bits, it results in a series of soft decision valuesrepresenting the second set of time domain portions.

The post-processor comprises a first channel decoder 522, a secondchannel decoder 524, and an output voice data interface 526. Preferably,the first channel decoder 522 and the second channel decoder 524 areViterbi decoders (as are the other channel decoders, preferably,discussed throughout). Also preferably, these channel decoders, e.g.,522, are memory 6, 7, or 8 coders. The first channel decoder 522 decodesthe soft decision values representing the first set of time domainportions to recover a representation of the first data stream 306. Thesecond channel decoder 524 decodes the soft decision values representingthe second set of time domain portions to recover a representation ofthe second data stream 308. The representations of the first data stream306 and the second data stream 308 are input into the interface 526.

Those skilled in the art will appreciate the variations that one mustmake in the receiver 110 depending upon variations made in thetransmitter 108 (as described in section "1." above). For example, if nochannels coders are used, there are no channel decoders. Symbol bysymbol decisions would be made. Also for example, if one channel coderis used, using one channel decoder that changes symbol timing from thefirst time portion to the second time portion may be used.

3. The UEP-DS-CDMA Transmitter: The VC UEP Method and Device

FIG. 6 shows a detailed block diagram of a UEP-DS-CMA transmitter 108that may be used in with the VC method. The pre-processor 200, the UEPprocessor 202, and the post-processor 204 will be described in orderwith reference to FIG. 6.

Referring to FIG. 6, the pre-processor 200 comprises input voice datainterface 600. The interface 600 separates the encoded voice data intotwo data streams, a first data stream 606 and a second data stream 608.Both the first data stream 606 and the second data stream 608 may, forexample, be represented by a series of bits.

The UEP processor 202 comprises a first channel coder 602, and a secondchannel coder 604. The first data stream 606 is input into the firstchannel coder 602 and the second data stream 608 is input into thesecond channel coder 604. The first channel coder 602 and the secondchannel coder 604 operate to form a first channel coded data stream 610and a second channel coded data stream 612, respectively.

In the preferred VC embodiment, the first channel coder 602 and thesecond channel coder 604 are different rate coders. This ensures thateach bit within the first channel coded data stream 610 is representedwithin a first time portion and each bit within the second channel codeddata stream 612 is represented within a second time portion. Each bit inthe first channel coded data stream 610 and the second channel codeddata stream 612 are of the same length. Each bit is also equal in lengthto T₀ (the basic time unit). Thus, the first channel coded data stream610 and the second channel coded data stream 612 are represented in thesame number of basic time units as the first data stream 606 and thesecond data stream 608.

The above example utilizes one half of the number of bits in the firstcoded signal 606 (e.g., the set of more significant bits) and one halfof the number of bits in the second coded signal 608 (e.g., the set ofless significant bits). A conventional rate 1/4 coder is used togenerate the first channel coded data stream 610 and a conventional rate1/2 coder is used to generate the second channel coded data stream 612.Thus, in effect, the average rate for the entire signal (comprising thefirst data stream 606 and the second data stream 608) is 1/3.

The post-processor 204 takes, as its inputs, the first channel codeddata stream 610 and the second channel coded data stream 612 and outputsan RF signal representing voice data input by the interface 600. Thepost-processor 204 comprises a multiplexer 614, an interleaver 616, aspreader 618, an modulator 620, an RF transmitter 622, and an antenna624, all connected as shown. The multiplexer 614 functions to combinethe first channel coded data stream 610 and the second channel codeddata stream 612. The combined signal is interleaved by the interleaver616 and spread by the spreader 618. The spread signal is modulated andtransmitted via modulator 620, RF transmitter 622, and antenna 624, asis conventional.

FIGS. 7a through 7d show the first data stream 606, the second datastream 608, the first channel coded data stream 610 and the secondchannel coded data stream 612. In this example, the first channel coder602 is a rate 1/4 coder and the second channel coder 604 is a rate 1/2coder. The outputs of these coders are shown in FIGS. 7c and 7d,respectively. Note that the total duration of the signals in FIGS. 7cand 7d equals the total duration of the signals in 7a and 7b. Thus, theVC UEP system, like the VT UEP system described above, also achieves UEPin a DS-CDMA environment. More specifically, this example achieves a"stretching" and "compressing" of bits in a different manner than theabove described VT system.

The processing of the signal shown in FIG. 7 is only exemplary. Onecould accomplish UEP with the first channel coder 602 and the secondchannel coder 604 having the same code rate but different errorcorrection capability (e.g., complexity).

Also, those skilled in the art will realize that one could:

(a) have more than two levels of significant bits (e.g., a first, secondand third level of significance) wherein each level has a differentamount of error protection provided to it;

(b) have the first channel coder 602 and the second channel coder 604 beany suitable combination of coders of different rates and notnecessarily a rate 1/4 coder and a rate 1/2, respectively;

(c) have any percentage of the bits (as opposed to 50% shown in FIG. 7)be deemed "more significant" depending upon the application and thecapabilities of the interface 600;

(d) stretch (e.g., by the rate of the first channel coder) the moresignificant bits while leaving the less significant bits unchanged orcompress the less significant bits (e.g., by the rate of the secondchannel coder) while leaving the more significant bits unchanged; and/or

(e) combinations of the above that do not conflict such as "(c)" and"(d)."

Preferably, the interleaver 616 symbol length is the basic time unit andthus, the interleaver 616 operates upon each basic time unit of thesignal shown in FIG. 7. However, those skilled in the art will realizethat one could have the interleaver 616 operate on symbols wherein thesymbol length is the length of:

(a) a chip and wherein the interleaving process performed by theinterleaver 616 is performed subsequent to the spreading function of thespreader 322; and/or

(b) a multiple integer of a chip or the basic time unit.

The output of the interleaver 616 goes into the spreader 618. Thespreader 618 represents a typical spreader for DS-CDMA applications asdescribed in the Gilhousen et al. article. The modulator 620, the RFtransmitter 622, and the antenna 624 are also typical of such elementsas described in the Gilhousen et al. article.

Preferably, the first channel coder 602 and the second channel coder 604are coders based upon rate compatible punctured convolutinal ("RCPC")codes as described in J. Hagenauer, N. Seshadri, and C-E. W. Sundberg,"The performance of rate compatible punctured convolutional codes fordigital mobile radio," IEEE Transactions on Communications 38(7),966-980 (July, 1990). In this case, the corresponding decoders wouldalso be based upon RCPC codes.

4. UEP-DS-CDMA Receiver: The VC Method and Device

FIG. 8 shows a block diagram of a UEP-DS-CDMA receiver 110. TheUEP-DS-CDMA receiver 110 comprises a pre-processor 800, a UEP processor802, and a post-processor 804.

Referring to FIG. 9, the pre-processor 800 comprises an antenna 900, anRF receiver 902, a demodulator 904, a despreader 906, a deinterleaver908, and a demultiplexer 910, all connected as shown. The outputs of thedemultiplexer 910 are input into the UEP processor 802. These are allconventional to the DS-CDMA coding art as described in the Gilhousen etal. article, with the exception of the demultiplexer 910. Thedemultiplexer 910 functions, in the above example, to separate the setof more significant time portions of the deinterleaved signal from theset of less significant portions of the deinterleaved signal. Thisresults in analog values that form a series of soft decision values thatare input into the UEP processor 802.

The UEP processor 802 comprises a first channel decoder 912 and a secondchannel decoder 914. These decoders, 912 and 914, receive, respectively,the series of soft decision values associated with the set of moresignificant portions of the deinterleaved signal and the series of softdecision values associated with the set of less significant portions ofthe deinterleaved signal. The series of soft decision values isprocessed with, preferably, a Viterbi decoder.

The post-processor 804 is comprises an output voice data interface 916.The interface 916 receives its inputs from the first channel decoder 912and the second channel decoder 914 and outputs a signal representativeof voice.

Those skilled in the art will appreciate the variations that one mustmake in the receiver 110 depending upon variations made in thetransmitter 108 (as described in section "3." above).

5. UEP-DS-CDMA Transmitter: The VP UEP Method and Device

The VP transmission method may be carried out in at least two basicembodiments. The first embodiment is shown in FIG. 10 and the secondembodiment is described as a variation thereof in FIG. 12.

Referring to FIG. 10, the VP transmitter comprises an input voice datainterface 1000, a first channel coder 1002, a second channel coder 1004,a multiplexer 1006, an interleaver 1008, a spreader 1010, a modulator1012, a variable power modulator 1014, an RF transmitter 1016, and anantenna 1018, all connected as shown. Essentially, the first channelcoder 1002, the second channel coder 1004, and the multiplexer 1006assist the signal from the interface 1000 to undergo UEP that will beprovided by the variable power modulator 1014.

The variable power modulator 1014 has as its input a signal wherein eachportion of the signal would be transmitted with the same amount of powerif the signal were processed using standard DS-CDMA techniques. However,the variable power modulator 1014 adjusts the amplitude levels (e.g.,providing amplitude modulation) of the more significant portions of thesignal with respect to the amplitude levels of the less significantportions of the signal such that the power used to transmit the moresignificant portions of the signal in higher than the power used totransmit the less significant portions of the signal.

Preferably, the average transmitted power of the signal will bepreserved so the power needed to transmit the signal will be the same asthe average power that would have been needed without this UEP scheme.This is preferable because the average co-channel interference, which isrelated to the average transmitted power of interfering users, remainsthe same. The required power control operates on the average transmittedpower for the VP technique.

While the preferred form of the VP device and technique have beendescribed, those skilled in the art will realize that variations of thepreferred form may include:

(a) using a first variable power modulator interposed between the firstchannel coder 1002 and the multiplexer 1006 and a second variable powermodulator interposed between the second channel coder 1004 and themultiplexer 1006 in lieu of the variable power modulator 1014 as shownin FIG. 12;

(b) using only one channel coder in lieu of the first channel coder1002, the second channel coder 1004 and the multiplexer 1006;

(c) using no channel coder in lieu of the first channel coder 1002, thesecond channel coder 1004 and the multiplexer 1006; and/or

(d) any combinations of the above that are compatible (e.g., "(a)" and"(b)").

6. UEP-DS-CDMA Receiver: The VP UEP Method and Device

Referring to FIG. 11, the VP receiver comprises an antenna 1100, an RFreceiver 1102, a demodulator 1104, a despreader 1106, a deinterleaver1108, a demultiplexer 1110, a first channel decoder 1112, a secondchannel decoder 1114, and an output voice data interface 1116, allconnected as shown.

In absence of any transmission impairment, the demodulator 1104 has asits input a signal wherein a first segment and a second segment of thesignal have a higher and lower power level, respectively. This is due tothe manner of transmission of the signal from the transmitter 108 asdiscussed in section "5." The UEP is obtained as a result of thevariable power introduced in by the variable power modulator 1014 of thetransmitter 108. The operation of the demultiplexer 1110, the firstchannel decoder 1112, and the second channel decoder 1114 provide aclear demarcation between the more significant bits and the lesssignificant bits. This should be appreciated by those skilled in theart. Those skilled in the art will also appreciate the variations thatone must make in the receiver 110 depending upon variations made in thetransmitter 108 (as described in section "5." above).

7. UEP-DS-CDMA: Combinations of VT, VC, and VP Methods

A number of different embodiments of achieving an UEP in a DS-CDMAsystem have been described above. These embodiments include VT, VC, andVP modulation/demodulation techniques. Those skilled in the art willrealize that combinations of these techniques may be in a single systemthat also achieves UEP in a DS-CDMA system. For example, one couldcombine VP and VT techniques in a single system. Also, one could combineVP and VC techniques in a single system. Also, one could combine VC andVT techniques. Finally, one could combine VP, VC, and VT techniques.

Although a number of specific embodiments of this invention have beenshown and described herein, it is to be understood that theseembodiments are merely illustrative of the many possible specificarrangements which can be devised in application of the principles ofthe invention. Numerous and varied other arrangements can be devised inaccordance with these principles by those of ordinary skill in the artwithout departing from the spirit and scope of the invention.

What we claim is:
 1. A method of processing a signal comprising applyinga spread spectrum coding process, the signal being a function of time,the improvement comprising:modulating the signal to generate a modulatedsignal, the signal comprising a first segment a second segment, thefirst segment being more significant than the second segment andcomprising a first time portion of the signal, the second segmentcomprising a second time portion of the signal, the modulating stepincreasing a duration of the first time portion relative to a durationof the second time portion.
 2. The method of claim 1 further comprisingspreading the modulated signal to generate a spread spectrum signal, thespreading comprising combining the modulated signal with a spreadingsignal.
 3. The method of claim 2 wherein said spreading step comprisesthe use of an orthogonal spreading sequence.
 4. The method of claim 1further comprising:(a) modulating a radio frequency carrier with aspread spectrum signal to generate a modulated radio frequency signal;and (b) transmitting the modulated radio frequency signal.
 5. The methodof claim 1 wherein the signal is generated by:(a) receiving an analogvoice signal at a transmitter; (b) coding the analog voice signal togenerate a digitized voice signal; (c) applying a forward errorcorrection code to the digitized voice signal to generate anintermediate signal; and (d) interleaving the intermediate signal togenerate the signal.
 6. The method of claim 5 wherein said interleavingstep comprises interleaving the intermediate signal based upon a basictime unit of the signal.
 7. The method of claim 1 wherein both the firstsegment and the second segment are modulated and wherein a durationincrease in the first time portion is the same as a duration decrease inthe second time portion.
 8. The method of claim 1 wherein said applyingthe spread spectrum coding process step comprises applying a codedivision multiple access coding process.
 9. The method of claim 8wherein said applying the code division multiple access coding processstep comprises applying a direct sequence code division multiple accesscoding process.
 10. An apparatus for processing a signal including meansfor applying a spread spectrum coding process, the signal being afunction of time, the improvement comprising:means for modulating thesignal to generate a modulated signal, the signal comprising a firstsegment and a second segment, the first segment being more significantthan the second segment and comprising a first time portion of thesignal, the second segment comprising a second time portion of thesignal, the means for modulating comprising means for increasing aduration of the first time portion relative to a duration of the secondtime portion.
 11. The apparatus of claim 10 further comprising means forspreading the modulated signal to generate a spread spectrum signal, themeans for spreading comprising combining the modulated signal with aspreading signal.
 12. The apparatus of claim 11 wherein the means forspreading comprises means for using an orthogonal spreading sequence.13. The apparatus of claim 10 further comprising:(a) means formodulating a radio frequency carrier with a spread spectrum signal togenerate a modulated radio frequency signal; and (b) means fortransmitting the modulated radio frequency signal.
 14. The apparatus ofclaim 10 wherein the signal is generated by:(a) means for receiving ananalog voice signal at a transmitter; (b) means for coding the analogvoice signal to generate a digitized voice signal; (c) means forapplying a forward error correction code to the digitized voice signalto generate an intermediate signal; and (d) means for interleaving theintermediate signal to generate the signal.
 15. The apparatus of claim14 wherein the means for interleaving comprises means for interleavingthe intermediate signal based upon a basic time unit of the signal. 16.The apparatus of claim 10 wherein the means for modulating modulatesboth the first segment and the second segment and wherein a durationincrease in the first time portion is the same as a duration decrease inthe second time portion.
 17. The apparatus of claim 10 wherein the meansfor applying the spread spectrum coding process comprises means forapplying a code division multiple access coding process.
 18. Theapparatus of claim 17 wherein the means for applying the code divisionmultiple access coding process comprises means for applying a directsequence code division multiple access coding process.
 19. A methodincluding applying a spread spectrum decoding method to a signal, thesignal being a function of time, the improvement comprising:variabletime demodulating the signal to generate a variable time demodulatedsignal, the signal comprising a first segment and a second segment, thefirst segment being more significant than the second segment andcomprising a first time portion of the signal, the second segmentcomprising a second time portion of the signal, the variable timedemodulating comprising increasing a duration of the second time portionrelative to a duration of the first time portion.
 20. The method ofclaim 19 wherein said variable time demodulating comprises:(a)despreading the signal to generate a despread signal; (b) deinterleavingthe despread signal to generate a deinterleaved signal; and (c)demultiplexing the deinterleaved signal to generate a first signal and asecond signal.
 21. The method of claim 20 further comprising:(a)generating a first series of soft decision values based upon the firstsignal; and (b) generating a second series of soft decision values basedupon the second signal.
 22. The method of claim 20 wherein saiddeinterleaving step comprises deinterleaving an intermediate signalbased upon a basic time unit of the signal.
 23. The method of claim 19wherein said variable time demodulating demodulates both the firstsegment and the second segment and wherein a duration increase in thesecond time portion is the same as a duration decrease in the first timeportion.
 24. The method of claim 19 wherein said applying the spreadspectrum decoding process step comprises applying a code divisionmultiple access decoding process.
 25. The method of claim 24 whereinsaid applying the code division multiple access decoding process stepcomprises applying a direct sequence code division multiple accessdecoding process.
 26. An apparatus including means for applying a spreadspectrum decoding method to a signal, the signal being a function oftime, the improvement comprising:means for variable time demodulatingthe signal to generate a variable time demodulated signal, the signalcomprising a first segment and a second segment, the first segment beingmore significant than the second segment and comprising a first timeportion of the signal, the second segment comprising a second timeportion of the signal, the means for variable time demodulatingcomprising means for increasing a duration of the second time portionrelative to a duration of the first time portion.
 27. The apparatus ofclaim 26 wherein the means for variable time demodulating comprises:(a)means for despreading the signal to generate a despread signal; (b)means for deinterleaving the despread signal to generate a deinterleavedsignal; and (c) means for demultiplexing the deinterleaved signal togenerate a first signal and a second signal.
 28. The apparatus of claim27 further comprising:(a) means for generating a first series of softdecision values based upon the first signal; and (b) means forgenerating a second series of soft decision values based upon the secondsignal.
 29. The apparatus of claim 27 wherein the means fordeinterleaving comprises means for deinterleaving an intermediate signalbased upon a basic time unit of the signal.
 30. The apparatus of claim26 wherein the means for variable time demodulating demodulates both thefirst segment and the second segment and wherein a duration increase inthe second time portion is the same as a duration decrease in the firsttime portion.
 31. The apparatus of claim 26 wherein the means forapplying the spread spectrum coding process comprises means for applyinga code division multiple access coding process.
 32. The apparatus ofclaim 31 wherein the means for applying the code division multipleaccess coding process comprises means for applying a direct sequencecode division multiple access coding process.
 33. An apparatus forprocessing a signal, the apparatus including means for applying a spreadspectrum encoding process to the signal, the improvementcomprising:means for applying a first error protection process to atleast one more significant portion of the signal, and a second errorprotection process to at least one less significant portion of thesignal, wherein the first error protection process provides a greateramount of error protection than the second error protection process, themeans for applying comprises means for applying a variable timemodulator.
 34. The apparatus of claim 33 wherein the means for applyingthe spread spectra encoding process comprises means for applying a codedivision multiple access coding process.
 35. The apparatus of claim 34wherein the means for applying the code division multiple access codingprocess comprises means for applying a direct sequence code divisionmultiple access coding process.
 36. The apparatus of claim 33, whereinthe means for applying further comprises at least one of:(a) means forapplying a variable power modulator, and (b) means for applying avariable rate coder.
 37. A method of processing a signal that applies aspread spectrum encoding process to the signal, the improvementcomprising:applying a first error protection process to at least onemore significant portion of the signal, and a second error protectionprocess to at least one less significant portion of the signal, whereinthe first error protection process provides a greater amount of errorprotection than the second error protection process, the step ofapplying comprises applying a variable time modulator to the signal togenerate an intermediate modulated signal.
 38. The method of claim 37wherein the step of applying the spread spectrum encoding processcomprises applying a code division multiple access coding process. 39.The method of claim 38 wherein the step of applying the code divisionmultiple access coding process comprises applying a direct sequence codedivision multiple access coding process.
 40. The method of claim 37,wherein the step of applying further comprises at least one of:(a)applying a variable rate coder to the signal to generate an intermediatemodulated signal; and (b) applying a variable power modulator to theintermediate modulated signal.